1. Field of the Invention
The present invention relates in general to a hard multilayer coating, and more particularly to such a hard multilayer coating having excellent wear resistance and tenacity.
2. Discussion of the Related Art
There is known a coated tool in which a tool substrate made of a cemented carbide or other material is coated at its surface with a hard coating formed of TiAlN. As an example of such a coated tool, JP-A-10-168583 (publication of unexamined Japanese Patent Application laid open in 1998) discloses a tool in which an interface layer formed of a relatively soft material such as CrN is interposed between the tool substrate and the hard coating formed of TiAlN, for the purpose of increasing a degree of adhesive or bonding strength with which the hard coating is bonded to the tool substrate. Further, JP-A-11-216601 (publication of unexamined Japanese Patent Application laid open in 1999) discloses a hard multilayer coating consisting of two types of TiAlN hard coating layers which have respective mixed compositions different from each other in crystal proportions of Ti and Al and which are alternately laminated.
However, since the TiAlN hard coating has a poor tenacity due to a large internal stress therein, the hard coating is likely to be chipped or separated from the tool substrate during a cutting operation, thereby making it impossible to sufficiently exhibit an excellent wear resistance of TiAlN. The provision of an interface layer or the superposing of two types of TiAlN hard coating layers which are different from each other in their mixed crystal proportions might somewhat prevents the chipping and separation, but does not satisfactorily prevents the chipping and separation.